Embryology Chapter 4: Intraembryonic Mesoderm

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Questions and Answers

What cells form the sclerotome during the differentiation of somites?

Nervous tissue cells

Muscle cells

Dermal cells

Cartilage and bone cells (correct)

Which structure is NOT derived from the lateral mesoderm?

Visceral layer of pleura

Somatic muscles of chest and abdomen

Involuntary muscles of heart

Kidneys (correct)

What is the primary role of the intermediate mesoderm in embryonic development?

Development of the kidneys and genital system (correct)

Establishment of the notochord

Creation of voluntary muscles

Formation of the dermis and skin

What process do neural crest cells undergo as they leave the neuroectoderm?

Epithelial-to-mesenchymal transition Signup and view all the answers

How many pairs of somites does the paraxial mesoderm typically form?

42-44 pairs Signup and view all the answers

What term is used to describe the cavity between the somatopleure and splanchnopleure?

Intraembryonic coelom Signup and view all the answers

Which component of the somites is responsible for forming the dermis of the skin?

Dermatome Signup and view all the answers

Why are neural crest cells referred to as 'the fourth germ layer'?

They contribute to multiple organ systems. Signup and view all the answers

At what week does the development of the head and neck begin in an embryo?

4th week Signup and view all the answers

How many pharyngeal arches are present in the developing embryo?

Six Signup and view all the answers

Which two of the following structures are formed from the first pair of pharyngeal arches?

Jaws Signup and view all the answers

What separates the pharyngeal arches on the external surface of the embryo?

Pharyngeal grooves Signup and view all the answers

Which of the following describes the primary components included in each pharyngeal arch?

Cartilaginous, arterial, muscular, and nervous components Signup and view all the answers

What is the fate of the 5th pharyngeal arch during development?

It regresses Signup and view all the answers

Which embryonic structures open towards the pharyngeal clefts?

Pharyngeal pouches Signup and view all the answers

What embryonic components separate the arches on the internal surface?

Pouches Signup and view all the answers

What are the two main prominences of the first pharyngeal arch?

Maxillary and mandibular prominences Signup and view all the answers

Which muscle is NOT derived from the first pharyngeal arch?

Stapedius Signup and view all the answers

What is the primary nerve associated with the second pharyngeal arch?

Facial nerve Signup and view all the answers

Which structure is derived from the third pharyngeal arch?

Greater horn of the hyoid Signup and view all the answers

The fourth pharyngeal arch gives rise to which type of cartilage?

Laryngeal cartilages Signup and view all the answers

What is the muscular derivative of the fourth pharyngeal arch?

Cricothyroid Signup and view all the answers

Which artery is associated with the third pharyngeal arch?

Common carotid artery Signup and view all the answers

Which feature is characteristic of the second pharyngeal arch?

Stapes as a cartilaginous component Signup and view all the answers

What vascular structure is derived from the sixth arch?

Proximal portion of the pulmonary arteries Signup and view all the answers

Which muscle is NOT derived from the sixth arch?

Cricothyroid Signup and view all the answers

The first pharyngeal pouch develops into which of the following?

Middle ear cavity Signup and view all the answers

Which nerve is associated with the sixth arch?

Recurrent laryngeal branch of the vagus nerve (CN X) Signup and view all the answers

Which structures are formed from the second pharyngeal pouch?

Palatine tonsils Signup and view all the answers

What does the fourth pharyngeal pouch develop into?

Superior parathyroid and ultimobranchial bodies Signup and view all the answers

Which of these is false regarding pharyngeal cleft 2, 3, and 4?

They develop into significant adult structures. Signup and view all the answers

What is the rudimentary structure of the fifth pharyngeal pouch commonly associated with?

Thyroid C-cells Signup and view all the answers

Study Notes

Intraembryonic Mesoderm

Formed by proliferation of cells in the primitive streak, separating the ectoderm and endoderm.
Develops lateral to the notochord into three longitudinal columns:
- Paraxial Mesoderm: Forms approximately 42-44 pairs of somites, which further differentiate into:
  - Sclerotome: Gives rise to cartilage and bone.
  - Myotome: Develops into muscles.
  - Dermatome: Forms the dermis of the skin.
- Intermediate Mesoderm: Contributes to the development of kidneys and the genital system.
- Lateral Mesoderm: Differentiates into:
  - Somatopleure: Forms voluntary muscles of the chest and abdomen, and the parietal layers of pleura and peritoneum.
  - Splanchnopleure: Forms involuntary muscles of the heart, bronchial tree, and gut, and the visceral layers of pleura and peritoneum.

Neural Crest Cells

Formed from cells at the lateral border of the neuroectoderm during neural tube development.
Undergo epithelial-to-mesenchymal transition, migrating into the mesoderm.
Vital for organ and tissue development, often referred to as the "fourth germ layer."

Development of Head and Neck

Initiated in the 4th and 5th week of embryonic development.
Mesenchymal tissue growth leads to the formation of pharyngeal arches and pouches, separated by clefts.
Six pharyngeal arches are formed; the 5th arch regresses, leaving five functional arches.
Notable structures arise from these arches including cartilaginous, arterial, muscular, and nervous components.

Derivatives of Pharyngeal Arches

First Arch:
- Comprises maxillary and mandibular prominences.
- Forms muscles of mastication and the mylohyoid.
- Associated artery: terminal maxillary artery.
- Innervated by branches of the trigeminal nerve.
Second Arch:
- Contains Reichart’s cartilage, precursor to stapes and hyoid components.
- Forms muscles of facial expression and stapedius.
- Associated arteries: stapedial and hyoid arteries.
- Innervated by the facial nerve.
Third Arch:
- Forms common carotid and internal carotid arteries.
- Cartilaginous components include lower body and greater horn of the hyoid.
- Nerve: glossopharyngeal nerve.
- Muscle: stylopharyngeus.
Fourth Arch:
- Gives rise to laryngeal cartilages, constrictors of pharynx, and other muscles.
- Associated artery: subclavian and aortic arch.
- Nerve: superior laryngeal branch of the vagus nerve.
Sixth Arch:
- Forms intrinsic laryngeal muscles (except cricothyroid).
- Associated with proximal pulmonary arteries and ductus arteriosus.
- Nerve: recurrent laryngeal branch of the vagus nerve.

Pharyngeal Clefts

Ectodermal-lined recesses between the pharyngeal arches.
Cleft 1: Develops into the external auditory meatus; the first pouch connects to the auditory/Eustachian tube.
Clefts 2, 3, and 4 typically overgrow due to the expansion of the second arch.

Pharyngeal Pouches

Endodermal-lined pockets forming between pharyngeal arches.
First Pouch: Develops into the middle ear cavity and Eustachian tube.
Second Pouch: Forms palatine tonsils, integral for the immune response.
Third Pouch: Generates thymus and inferior parathyroid.
Fourth Pouch: Develops the superior parathyroid and ultimobranchial bodies.
Fifth Pouch: Rudimentary, contributes to the thyroid C-cells.

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Description

Explore the development of the intraembryonic mesoderm, formed by the proliferation of cells in the primitive streak. This chapter analyzes the separation of ectoderm and endoderm and the formation of the paraxial mesoderm and somites during embryonic development.